(1) Field of the Invention
The present invention relates to a novel and highly advantageous process of inhibiting scale formation in aqueous media and more particularly to such a process by using a preparation containing cyclohexane-1,2,3,4-tetracarboxylic acid obtained in a simple and highly economical manner, to a process of producing such a preparation, and to a composition containing said cyclohexane-1,2,3,4-tetracarboxylic acid.
(2) Description of the Prior Art
It is known to add to aqueous media polyphosphates and/or, more recently, phosphonic acids in order to prevent precipitation of alkaline earth metal ions. See German Published Applications No. 1,216,471 and No. 1,469,253. Phosphonic acids are in general preferred over polyphosphates because they are stable against hydrolysis and, therefore, retain their effectiveness even in acid or alkaline media. It is also known that, when using phosphonic acids, it is sufficient to add substoichiometric amounts in order to keep in solution the hardness-forming agents of water. This use of substoichiometric amounts is generally known as threshold effect or also as "seed effect" (see Ralson in "Journal Petroleum Technology" volume 21 (1969), page 1029 to 1036).
Since nitrogen- and phosphorus-containing agents have been held responsible for eutrophication of rivers, lakes, and, in general, of bodies of water, many attempts have been made to find new compounds with threshold activity which are free of nitrogen and phosphorus.
Heretofore, two classes of compounds containing neither nitrogen nor phosphorus which are effective in substoichiometric amounts have become known. These compounds are either polymers of the most varied composition as described by Elliot in "Desalination" Vol. 8 (1970), pages 221 to 236 and, on the other hand, modified polysaccharides, for instance, starches which have been degraded by acid means or by oxidation. See, for instance, German Pat. No. 1,810,571 and German Published Application No. 1,925,235.
Both types of seed substances, however, are effective only in higher concentrations than those in which the phosphonic acids are employed.
Furthermore, it is known that cyclohexane-1,2,3,4,5-pentacarboxylic acid has such a threshold activity (see German Published Application No. 2,132,802).